1. Field of Invention
The present invention relates to a method and apparatus for selectively correcting the skewing of data lines between network devices. More specifically, a technique is applied to deskew the bit lines of a wide bus to guarantee the alignment of the lines with respect to a system clock.
2. Description of Related Art
A bus, as used in a network device, is a set of parallel conductors, which allow devices attached to it to communicate with each other. A bus usually consists of various lines, some of which allow for the flow of data and other lines that allow for control. As network devices have been operated at higher frequencies, problems can occur with the buses that were not evident in the buses at lower frequencies. One problem that occurs is the skewing of data in the bus; i.e. where different data lines in the bus have different alignments with respect to each other and a system clock.
There are several possible ways to introduce skew: PC board traces, temperature, different processes and data recovery circuitry. The longest distance of skew could well over +/−1 bit, but not likely to have skew greater than +/−2 bits. For buses operating at lower frequencies, such problems of skew were easier to solve because the lower frequency allowed for more “time” for correction. Additionally, the advent of wider buses can allow for even greater skewing between data in a first data line and a sixteenth data line, for example.
Thus, there is a need for a method and a mechanism in a network device that allows for data lines to be deskewed, especially for wide buses operating a high frequencies. Additionally, there is also a need for a process of deskewing data which can be either automatic or manually controlled and alos allow for monitoring of the skewing of data in the bus.